As he entered the section of track where the derailment occurred, the train slowed down well below the 50 mph speed limit.

"We're going fairly slow through here today. That's all the old track over there," Trent said.

Meanwhile, the National Transportation Safety Board is backing off its stunning revelation that the doomed train may have been hit by a rock or some other projectile that might have distracted the train's engineer.

This softball-sized crack seems to show that something may have hit the windshield. Two other local trains, not far from the derailment, were also bombarded with projectiles that same night.

In an audio transmission, an engineer said, "An unknown object made contact with that train shattering the windshield."

NTSB head Robert Sumwalt downplayed the significance on Face the Nation.

Bob Scheiffer asked, “Is there any way that that may have been connected to the crash in some way?”

Sumwalt replied, “It could be completely coincidental, or it could be causal and that's what we intend to find out.”

Scheiffer then asked, “You know, it could have been that somebody shot at that train?”

Sumwalt replied, “You know, I’d like to downplay that part of it. Looking at the fracture pattern it looks like something about the size of a grapefruit if you will and it did not even penetrate the windshield.”

YouTube is filled with videos of people throwing rocks at various trains.

Amtrak conductor Michael Callanan once worked the same route as the fatal train.

He told Trent, "It does happen quite a bit. People throw rocks at the train. You'll see it hit the window. It is just a big bang."

Now, the FBI is investigating whether someone threw a rock or other projectile at the windshield of the New York-bound Amtrak train that derailed outside Philadelphia.